Article palletizers are well known in the art. See e.g., U.S. Pat. No. 3,934,713.
In general palletizers receive randomly placed articles such as upstanding containers en masse along a conveyor pathway, separate successive charges of articles from said mass, form the charge into an ordered group according to a pattern at a pattern forming area, and then sweep the charge further downstream to form a layer on a pallet. A separator sheet, usually of thin chipboard, is then placed over the charge, the pallet is indexed downward by a hoist a distance corresponding approximately to the height of the articles, and a next charge of articles is swept into place as the next layer. After n charges forming n layers are in place, a last separator sheet is placed on top and a top frame, usually of wooden construction, is placed on top. The loaded pallet may then be bound around its upper and lower edges to sufficiently stabilize the load for shipping and handling.
Such a prior art palletizer typically has at least three distinct subsystems: (1) a sweep subsystem for sweeping n successive charges of articles from the pattern forming area onto the pallet to stack up to n layers; (2) a carriage subsystem for retrieving not only chipboard sheets one at a time from a supply thereof and placing them one at a time in an interleaved fashion between the layers in said stack, but also for retrieving the top frame from a supply thereof and placing the top frame on the finished stack; and (3) a hoist subsystem for lifting the pallet up to alignment with the pattern forming area and then indexing the pallet back down one layer thickness at a time as successive layers are swept thereon. The three subsystems are typically controlled by routine motor control devices such as for example magnetic motor starters and variable frequency inverters such as an E-TRACK.RTM. sold by TB Woods.
Such prior art palletizers can have substantial difficulty in attaining the speeds desirable in today's commercial environment. For example, such a palletizer may work reasonably well at 1,000 cans per minute, but at speeds approaching 1,400 cans per minute or higher, such a palletizer may become inadequate. If the machine components are strengthened with heavy duty materials, the inevitable increased weight can be counterproductive with respect to speed.
Also, prior art palletizers often use vacuum operated suction cups mounted on the carriage and operated with routine control circuitry to grasp the chipboard sheets for transfer to and placement on the stack one at a time. However, such suction cups can become clogged with debris and other contaminants over a period of use, thereby reducing their effectiveness and reliability. Such clogging problems become more pronounced as machine speed is increased.
Also, prior art palletizers typically use the carriage to retrieve the top frame from a supply thereof while a loaded pallet is being changed out in exchange for an empty pallet. The changeout time is used to pick up the top frame; however, the carriage will then carry the top frame along with the carriage back and forth while all n separator sheets are being placed. This procedure adds to the operating weight of the carriage and can reduce speed even further.